Human beings, especially elderly persons, frequently tend to lose vision due to a gradually increasing clouding of the natural lens of the eye, which results from the development of a degree of opacity or clouding of the fibers (the cortex) surrounding the inert nucleus of the natural lens within the capsular bag housing the same. The condition where this opacity spreads into the center of the lens in the region behind the pupil so as to impair vision, is designated cataract. When the opacity has progressed sufficiently to cause the loss of useful functional vision, the cataract is said to be mature, and the only currently available treatment for that condition is the removal of the cataract by extraction of the lens from the eye and the replacement of the natural lens by an artificial lens. Such a cataract removal, which is probably one of the most common and widely performed ophthalmic surgical procedures these days, may involve either an intracapsular or an extracapsular extraction of the natural lens.
In an intracapsular cataract extraction (ICCE), the entire lens, including the nucleus, the cortex (the fibers) and the enveloping capsular bag, is taken out as a unit, with the zonular fibers which connect the bag to the ciliary body being first dissolved and the cataract then being removed with the aid of a suitable tool such as a low temperature probe (cryoadhesion) or an erysiphake. In such a case, the removal procedure is usually followed by the implantation of an intraocular lens (IOL) into the anterior chamber of the eye, with the lateral position fixation elements or haptics of the IOL (resilient loops, arms, or the like) being received in the angle of the anterior chamber (the angle is the groove or channel defined between the cornea in the limbal region thereof and the outer periphery of the iris where it joins the choroid coat). As an alternative, it has also been proposed to implant the IOL in the posterior chamber, with the haptics being received in the ciliary sulcus (the groove or channel defined at the juncture between the iris and the ciliary body), but this is always subject to the provision that steps are taken to ensure that the IOL does not come loose and fall into the vitreous humor.
In an extracapsular cataract extraction (ECCE), by way of contrast, first a major portion of the anterior capsule is cut away, leaving in place only that residual part of the capsular bag which consists of the posterior capsule and the remaining annular anterior capsular flap, then the lens nucleus is extracted from the capsular bag by any well-known type of expression or by phacoemulsification, and finally the cortex is removed by irrigation and aspiration. In such a case, the removal procedure is usually followed by the implantation of an IOL into the posterior chamber of the eye, with the haptics then being seated either in the ciliary sulcus outside the residual capsular bag, so that the entire residual capsular bag isolates the IOL from the vitreous humor, or physically within the residual capsular bag at the equatorial region thereof where the anterior capsular flap adjoins the posterior capsule, so that only the posterior capsule of the residual capsular bag isolates the IOL from the vitreous humor.
Many designs of intraocular lenses have been developed over the past 30-40 years. Representative ones are shown in Kelman U.S. Pats. Nos. 4,092,743, 4,174,543 and 4,608,049; Hoffer U.S. Pat. No. 4,244,060; Poler U.S. Pat. No. 4,402,579; Ginsberg et al. U.S. Pat. No. 4,562,600; Mazzocco U.S. Pat. No. 4,573,998; Sayano et al. U.S. Pat. No. 4,681,585; Smith U.S. Pat. No. 4,704,123; Anis U.S. Pat. No. 4,795,460; Goldberg et al. U.S. Pat. No. 4,806,382; and Choyce U.K. Pat. No. 2,081,469. Irrespective, however, of whether anterior chamber implantation or posterior chamber implantation or both has been the goal (posterior chamber implantation is by far the currently favored method), much of the emphasis in the development of intraocular lens designs has been on the forms and physical properties of the haptics, especially with regard to achieving an optimum haptic strength and flexibility, on the one hand so as to enable the optic to be implanted easily through a scleral, limbal or corneal incision and in a properly centered position in the eye, and on the other hand so as to ensure that the IOL is firmly seated in the eye secure against both dislodgement and rotation.
In addition to the IOL constructions proposed by the above-mentioned patents, Siepser U.S. Pat. No. 4,556,998 proposed a hydratable IOL which can be made in the form of a dehydrated solid body very small in size (e.g., 2-4 mm in diameter) and either having or being devoid of haptics. Following an extracapsular cataract extraction, the lens body, while still in its dehydrated state, is implanted in the residual capsular bag through a minimal size (e.g., 3 mm) corneal, scleral or limbal incision and is there hydrated by the natural fluid of the eye (the aqueous humor) and caused to swell to its desired size and optic power. The design of this IOL was aimed at achieving a proper positioning of the IOL and avoiding the exertion of undue pressure on the surrounding eye tissues.
To the extent necessary for an understanding of the present invention, therefore, the disclosures of these patents are incorporated herein in full by this reference.
While posterior chamber IOLs have proven to be of great benefit to persons who have undergone an ECCE, some post-operative complications do occasionally arise in connection therewith. One such complication is a post-implantation clouding of the posterior capsule which is a consequence of the fact that some epithelial cells are almost invariably left in the equatorial region of the capsular bag and not removed therefrom during the irrigation and aspiration phase after the surgeon has extracted the cataract. These cells have a tendency to migrate over the anterior surface of the posterior capsule toward the center or optic region thereof and, upon accumulating there, lead to capsular fibrosis and the formation of Elschnig's pearls, which in turn causes opacification of the posterior capsule and ultimately impairs vision in the same manner as the original cataract did, namely, by blocking the passage of light through the capsule to the retina. To remedy this situation, a further surgical procedure then becomes necessary, which may involve scraping and cleaning the accumulated fibers from the anterior surface of the posterior capsule behind the implanted IOL and possibly even a cutting out of the opacified region of the posterior capsule by means of a laser capsulotomy (which of late has substantially supplanted knife discission as the standard operating procedure). In any event, the possibility that the patient may be traumatized or even develop retinal detachment by such a procedure, coming after the patient has already gone through two losses of vision and one or two surgical procedures (the ECCE and the IOL implantation), is a prospect to be avoided.
The problems of capsular fibrosis and formation of Elschnig's pearls and of the resultant opacification of the posterior capsule following an ECCE have been recognized in the technical and patent literature; see, for example, the discussions thereof in the aforementioned U.S. Pats. Nos. 4,244,060 (Hoffer) and 4,562,600 (Ginsberg et al.). However, neither the ridged Hoffer lens nor the flanged Ginsberg lens described in those patents has been successful in eliminating these problems, in essence for the reason that in each of these lens designs one or more recesses are formed in the ridge or flange which projects posteriorly from the lens optic and is in contact with the front or anterior surface of the posterior capsule once the IOL has been implanted. Hoffer taught that such recesses (which are designated by reference numeral 34 in U.S. Pat. No. 4,244,060) are useful because they facilitate performance of a knife discission of a clouded posterior capsule without necessitating a dislodgement of the IOL. Ginsberg et al. taught that such recesses (which are designated by reference numerals 34 and 36 in U.S. Pat. No. 4,562,600) are useful because they facilitate rotational positioning of the IOL during the initial implant surgery and also minimize the post-implantation occurrence of unwanted and disturbing light reflections into the visual field. However, such recesses constitute breaches or gaps in the ridge or flange element of the lens which actually permit that which the ridge or flange of the lens is norminally intended to inhibit, namely, the migration of the epithelial cells into the optic region of the posterior capsule from the equatorial region of the capsular bag. The Hoffer patent evidences no awareness of this problem at all and thus offers no solution therefor whatsoever, while the Ginsberg et al. patent, though recognizing the possibility of cell migration through the notch-like recesses in the lens flange, suggests only the substitution of somewhat smaller indentations or of round holes for the notches, which still leaves one or more gaps in the flange through which cells can migrate.
In both the Hoffer and Ginsberg lenses, furthermore, the ability of the epithelial cells to migrate from the equatorial region of the capsular bag toward the optic region of the posterior capsule is not inhibited in any way until the cells are practically in the optic region, i.e., when they reach the zone of contact of the ridge or flange with the posterior capsule. In the Hoffer lens, on the one hand, this is so because the hairs constituting the haptic structure of the lens, though they are received in the cleft or fornix of the capsular bag, do not exert mechanical pressure on the entire interior surface of the equatorial region of the bag. Thus, not only are there many locations where the cells are not killed by mechanical pressure, but the Hoffer lens actually relies of the presence of the cells and the resultant fibrosis to anchor the IOL in the capsular bag. At the same time, the haptic structure, by virtue of the very nature of the hairs, cannot ensure that the rim portions and the ridge of the lens are pressed against the posterior capsule to block the migration of the epithelial cells into, and hence the propagation of capsular fibrosis and the formation of Elschnig's pearls in, the optic region of the posterior capsule. In the Ginsberg lens, on the other hand, the haptics cannot even partially inhibit cell migration because they are seated in the ciliary sulcus outside the capsular bag, while at the same time they cannot fully ensure adequate pressure contact between the flange of the IOL and the posterior capsule, so that again capsular fibrosis and pearl formation are not inhibited. Moreover, by virtue of the fact that in both the Hoffer lens and the Ginsberg lens there is an open space defined between the posterior capsule and the rear or posterior face of the optic, pearl formation in the optic region of the posterior capsule is not only not inhibited but is actually promoted. 0f course, even were the haptics of the Ginsberg lens seated in the capsular bag, they would still not serve to block cell migration over the entire circumferential extent of the equatorial region of the bag.
In this connection it has also been shown that the use of haptics of the type (J, C and like-shaped arms or loops) shown in the Ginsberg patent, which are generally made appreciably longer, viewed diametrally of the optic, than the diameter of the capsular bag in the equatorial region thereof, entails certain drawbacks.
On the one hand, when such a lens is being implanted, the surgeon generally first seats one haptic, e.g., the inferior or lower haptic, in the equatorial region of the bag, e.g., at the 6 o'clock position, behind the proximate portion of the anterior capsular flap and then deflects the superior or upper haptic downwardly a bit (i.e., toward the optic) in an attempt to move it past the edge of the flap toward the posterior capsule before releasing the haptic to permit it to snap back to its full height in the equatorial region of the bag, e.g., at the 12 o'clock position. The risk in this procedure is that it may lead to the phenomenon of "capsular tuck" in which the deflected haptic, upon being released, does not clear the capsular flap but instead catches it and in effect tucks it back against the front face of the posterior capsule, by virtue of which the possibility of migration of epithelial cells from the equatorial region of the bag onto the optic region of the posterior capsule is enhanced.
On the other hand, since the length of these haptics exceeds the bag diameter, they can exert relatively high stresses on the equatorial region of the bag. The haptics, therefore, even if they do not tear through the capsular tissue in the equatorial region (which is always a risk, especially if the equatorial region has been weakened somewhat or even perforated during the surgical extraction of the cataract), can cause the anterior capsular flap to "unfurl," i.e., to be displaced radially outwardly of the posterior capsule. Such unfurling brings a portion of the equatorial region of the anterior capsular flap into substantially coplanar alignment with the posterior capsule and hence provides an even better access for cellular migration and proliferation onto the optic region of the posterior capsule.
The aforementioned U.S. Pat. No 4,795,460 (Anis) proposed an intraocular posterior chamber lens which, for the purposes of ease of implantation and secureness of positioning, has a pair of identically sized and shaped 2-ended haptic loop members disposed in parallel planes and extending in opposite directions each around somewhat more than one half (180.degree. +) of the perimeter of the optic, the two ends of one member being secured to the optic substantially tangentially thereof at the 3 o'clock position and the ends of the other member being correspondingly secured to the optic at the 9 o'clock position. The loop members are stated as defining a generally continuous circular periphery adapted to engage the periphery of the capsular bag over substantially 360.degree., by virtue of which the IOL assertedly can be implanted in any position and is secured against inadvertent dislodgement. The patent is entirely silent, however, on the problem of post-implantation posterior capsular fibrosis, pearl formation and opacification and expresses no awareness of the problem of unfurling of the anterior capsular flap and its contribution to posterior capsular opacification. In point of fact, the location of the loop members in two adjacent planes and their joint generally single-diameter locus does not afford an adequate barrier to epithelial cell migration.